When printing is performed on a surface of a non-absorptive printing object, such as a plastic film, a coated paper, or a laminated paper, according to an inkjet printing method, an inkjet ink that has undergone printing is generally heated and dried.
However, recently, inkjet inks, such as HEATLESSINK (registered trademark), have been developed and have been coming into practical use, which are capable of excluding a heating/drying step by being provided with quick-drying properties that result from the fact that only an organic solvent is used as a solvent or from the fact that a so-called organic solvent rich state in which an organic solvent is larger in quantity than water is reached even when water is used together as a solvent.
Additionally, recently, various studies have been made to perform printing that is more excellent in fixability than before by using such a quick-drying inkjet ink for a polyolefin-based printing object, such as a polypropylene film or a polypropylene laminated paper or the like, which has difficulty in excellent in fixability printing particularly because of small polarity, among the non-absorptive printing object.
For example, PTL 1 proposes that a polyamide resin that serves as a binder and at least one kind selected from the group consisting of a terpene phenol resin, a dicyclopentadiene resin, and a rosin ester each of which serves as a tackifier that gives tackiness to the polyamide resin so as to improve printing fixability with respect to a printing object should be compounded together in a quick-drying inkjet ink.
PTL 2 proposes that two kinds of polyamide resins having mutually-different acid values and a rosin-modified maleic acid resin and/or a terpene phenol resin serving as a tackifier should be compounded together.
PTL 3 proposes that a polyamide resin, a rosin-modified maleic acid resin that serves as a tackifier, and a titanium chelate should be compounded together.
However, disadvantageously, in any of the conventional quick-drying inkjet inks of Patent Documents 1 to 3 or the like, precipitation is liable to occur because stability is insufficient during ink storage, or blurring etc. is liable to occur when printing is restarted because a nozzle of an inkjet printer is clogged at the decapping time of printing in addition to the fact that printing fixability with respect to a polyolefin-based printing object or the like still cannot be improved satisfactorily.
The term “decapping time” denotes a period of time during which an inkjet ink in a nozzle among a plurality of nozzles provided in an inkjet printer is exposed to the open air in a standby state in which ink droplets are not discharged in accordance with a printing pattern in intermittent printing.
An inkjet printer is generally provided with a function to close a nozzle (to cap a nozzle) so as not to cause clogging that results from the fact that an inkjet ink in the nozzle is exposed to the open air and is dried ordinarily when the operation of the inkjet printer is being stopped.
However, such capping is released when printing is performed, and therefore a nozzle, which is in a standby state particularly when intermittent printing is performed, remains in a state (decapping state) in which the nozzle is not closed until ink droplets are discharged next time, and the inkjet ink in the nozzle is continuously exposed to the open air during that time. Therefore, there is a tendency for the nozzle to be clogged more easily in proportion to an increase in this period of time, i.e., in proportion to an increase in the duration of the decapping time.
Hereinafter, a feature characterized in that the nozzle is not easily clogged for the decapping time is evaluated in terms of whether “intermittent printability” is excellent or not. An inkjet ink can be evaluated as becoming more excellent in intermittent printability in proportion to an increase in the duration of a decapping time during which clogging is not caused.